Recording materials containing an electron-donating colorless dye and an electron-accepting compound have heretofore been used as a pressure-sensitive paper, a thermal paper, a light-sensitive pressure-sensitive paper, an electric thermal recording paper, a thermal transfer paper and others. For instance, the details of such materials are described in British Patent No. 2,140,449, U.S. Pat. Nos. 4,480,052 and 4,436,920, JP-B-60-23992, JP-A-57-179836, JP-A-60-123556 and JP-A-60-123557. (The terms "JP-A" and "JP-B" as used herein mean an "unexamined Japanese patent application" and an "examined Japanese patent publication", respectively.) In particular, a thermal recording material is described in detail in JP-B-43-4160 and JP-B-45-14039. Thermal recording systems are used in various fields for facsimiles, printers and labels, and the need for them is increasing.
However, since a thermal recording material involves the drawbacks that it is often fogged with solvents and its colorant is often faded with oils, fats or chemicals, its commercial value is lowered, especially in the field of labels, vouchers, word processor papers and plotter papers. The present inventors have studied electron-donating colorless dyes and electron-accepting compounds, to develop good constituent raw materials for recording materials, as well as good recording materials themselves, with respect to oil solubility, water solubility, partition coefficient, pKa, polarity of substituents, and position of substituents of such dyes and compounds. It has been found, however, that materials which are hardly fogged with solvents are often faded with oils, fats and chemicals, while those which are hardly faded with oils, fats and chemicals are often fogged with solvents.